Synthesis, crystal structure, and spectral studies of 10-(2-Benzothiazolylazo)-9-phenanthrol

10-(2-Benzothiazolylazo)-9-phenanthrol (L) is prepared by a reaction of 2-hydrazinobenzothiazol with 9,10-phenanthrenequinone. The crystal and molecular structure of the L·CHCl3 solvate is determined by X-ray diffraction. The data of the X-ray diffraction study, as well as IR, 1H NMR, and electronic absorption spectra, indicate that in the crystal state and solutions the L molecule exists in the form of a quinohydrazone tautomer (b) (s-trans, cis) stabilized by the intramolecular N2-HN2…O1 hydrogen bond. The "mobile" H atom is located at the N2 atom of the azo group. The benzothiazolyl and phenanthrenequinone fragments are nearly coplanar. Spectroscopic criteria for the state of L in various media are determined based on the data of IR, 1H NMR, and electronic absorption spectroscopy and the results of the Pariser-Parr-Pople quantum-chemical calculations.